Deep sea mining involves collecting mineral deposits, such as polymetallic nodules, diamonds, gold, and rare soils from (below) the sea floor at large depths. Polymetallic nodules may for instance comprise nickel, copper, cobalt and manganese nodules. In deep sea mining, the sea floor may be a distance of up to 5000 m and more away from the sea surface, and developing a mining vehicle for collecting the nodules at such depths imposes many challenges.
Deep sea mining vessels need to bring a subsurface mining vehicle to the sea floor and recover the same from the sea floor after termination of a mining operation. Typical vessels thereto comprise some type of launching and docking device that is operated from a docking well. A docking well typically passes through and is enclosed by the vessel hull, and opens to the sea at its bottom side defining a so-called splash zone of the docking well. The docking well may be closable across the bottom by movable gates if desired. It is also possible to launch a mining vehicle over a side edge of the vessel, in which configuration the launching and docking device operates from said side edge of the vessel. The wording ‘docking well’ in the context of the present application also comprises any side wall of the vessel. A deep sea mining vessel further typically comprises a pumping arrangement for bringing mined mineral deposits from the sea floor to a vessel storage hold through a transport pipe system. A riser string extends from the vessel to the mining vehicle to convey the mined mineral nodules towards the sea surface. A lift system is usually operational in raising and launching the riser string.
WO 2007/135399 A1 discloses a device for launching equipment from a vessel. Typical equipment includes Christmas trees for coupling to a seabed wellhead, BOP stacks, intervention systems, and subsea processing equipment such as pumps, and manifolds. The prior art device comprises a docking frame or cradle, that is located on deck of a vessel and can be translated over rails provided on deck. The cradle is hinge mounted to the vessel and can be tilted between a substantially horizontal equipment docking position and a substantially vertical launching position. The cradle comprises a carriage for guiding the equipment along a longitudinal direction of the cradle.
U.S. Pat. No. 8,430,049 B1 discloses a launch and recovery system for a vehicle. A frame is tilted with respect to a vessels deck, such that a rear end of the frame is below the water surface. The frame carries an intercepting vehicle that is lowered into the water by towing out a line with the aid of a winch. The vehicle to be launched or retrieved is attached to the intercepting vehicle.
In launching subsurface mining vehicle, the maximum environmental circumstances are often limited to certain wave heights, and considerable time is lost while waiting for a weather window for deploying or recovering the vehicle. Further, most damages to subsea mining vehicle occur during launching and recovery. Given the size, complexity and cost of a mining vehicle, this is unacceptable.
The above described disadvantages occur to an even higher extent in launching and recovering subsurface mining vehicle. Such a deep sea mining vehicle indeed is configured to move across a sea floor when collecting nodules and the ratio of the vehicle's submerged weight to its sea floor contact surface should preferably be lower than 6,90 kPa (or about 690 kg/m2). A deep sea mining vehicle therefore has a relatively low weight combined with a relatively large contact surface. This makes it difficult to control the vehicle during launch when suddenly contacting a moving mass of water, or to grab the vehicle during a recovery operation. The risk for collision with parts of the vessel or other structures is high.
Therefore, an aim of the present invention is to provide a device and method for launching subsurface mining vehicle into a water mass and/or recovering the vehicle from the water mass in a more controlled manner.